The present invention relates to a slot antenna.
Slot antennas have found wide application in the field of radio communication. Conventional slot antennas comprise halfwave elements. This has put them at a disadvantage, with regard to size, compared with patch or wire antennas, such as the PIFA (planar inverted-F antenna), which can be constructed with quarterwave elements.
Ideally, a wire monopole antenna or the like comprises a quarterwave radiating element perpendicular to an infinite ground plane. This configuration is in practice impossible to achieve. However, in some circumstances, such as a mobile phone, it is impossible even to approximate this configuration well because of other design constraints.
An object of the present invention is to provide a slot antenna that is not at a size disadvantage to PIFA antennas.
According to the present invention, there is provided a resonant monopole slot antenna including a radiating slot which is dimensioned such that the slot is equivalent electromagnetically to an odd number of quarter wavelengths at the antenna""s operating frequency, wherein the antenna""s feed is arranged at the open end of the radiating slot. Feeding the slot at it open end provides a broader usable bandwidth than feeding at a position towards the closed end.
The radiating slot may be straight or not straight. If the slot is not straight, it may be, for example, L-shaped or meander.
Preferably, said odd number is 1.
Preferably, the radiating slot comprises an area of a printed circuit board which is free of conductor. More preferably, said area extends to an edge of the printed circuit board.
Preferably, said feed comprises a conductor extending transversely across the radiating slot at its open end. More preferably, said conductor comprises a signal line of a stripline or microstrip transmission line.